A variety of composite materials are made by bonding into a unitary product a primary constituent, often a structural or reinforcement component, using a bonding agent or matrix material, such as an adhesive resin. Composites include engineered wood products (wood-adhesive composite products), insulation products and the like.
Wood-adhesive composite products (i.e., wood composite products), in particular, are used in a wide variety of applications. Regardless of their particular construction, wood composite products (wood composites) often exhibit superior properties to solid wood of similar dimensions. Wood composites are generally stronger, usually exhibit better resistance to degradation and failure, and often are more cost-effective than solid wood alone.
Wood composites, such as plywood, laminated veneer lumber (LVL), oriented strand board (OSB), oriented stand lumber (OSL), waferboard, chipboard, particleboard, flakeboard, medium density fiberboard, hardboard and the like are made by bonding together wood components, be they wood veneers in the case of plywood and LVL, wood strands in the case of OSB and OSL, wood flakes in the case of waferboard, or smaller wood particles in the case of wood composites such as particleboard, etc., using a variety of adhesives, both synthetic adhesives, usually petroleum-based adhesives, and natural adhesives, usually protein-based adhesives.
A feature common to the use of almost all of these adhesives is that the binder, either as a liquid or as a powdered solid, is spread on to or otherwise mixed with the primary constituent (substrate material), for making the composite, such as wood components used to assemble wood composite products. Thereafter, the mixture of the adhesive and the primary constituent of the composite (substrate material) is consolidated into a unitary product, usually using heat to cure the adhesive and often using pressure to increase its density and strength. For example, in the case of wood composite products, the wood components are usually formed into a stack or mat which is then consolidated in a hot platen press to cure the adhesive.
The prior art also has sought ways for accelerating the curing rate and/or enhancing the bonding properties of these adhesives, particularly for making wood composites. For example, U.S. Pat. No. 4,915,766 describes the use of certain acetone-formaldehyde resins as a cure rate accelerating additive for phenol-formaldehyde resins used as an adhesive for wood composites, particularly for making plywood.
More recently, there has been increasing interest in developing ways for reducing formaldehyde emissions associated with the production and use of building materials, including a focus on developing non-formaldehyde based wood adhesives.
US Pub 2007/0054144 describes a non-formaldehyde-based, thermosetting adhesive useful as a wood adhesive. The adhesive comprises a resin having azetidinium functional groups and can be made by reacting an epoxide, such as epichlorohydrin, with a polyamide resin, particularly the reaction product of a dicarboxylic acid, such as adipic acid, and a polyalkylene amine, such as diethylenetriamine. Wood composite products of acceptable properties can be prepared using such azetidinium functional adhesives. Unfortunately, the need to keep the adhesive at a low (acid) pH, usually a pH of about 3-4, to maintain acceptable stability during storage, transportation and use, gives rise to potential corrosion problems with this adhesive.
Indeed, the development of new composites and new techniques for manufacturing such composites that can be used for example in construction applications, particularly those that have the potential for reducing volatile emissions, including formaldehyde emissions, remains a continuing goal of the industry.
The present invention provides a non-formaldehyde containing additive that can be used for formulating non-formaldehyde-based adhesives for manufacturing a wide variety of composites, particularly wood composites.
The non-formaldehyde containing additive also can be used in connection with formaldehyde-based adhesives in a way to reduce formaldehyde emissions without sacrificing the adhesives' ability to produce composites with acceptable properties.